Explained: Reading the Life Signature on Venus

Artistic impressions of Venus, after the confirmation of phosphine in the atmosphere. On the left, a representation of phosphine molecules in the inset. (ALMA, JCMT, ESO, NASA / JPL / Caltech via ESO)

An announcement by an international team of astronomers about the discovery of phosphine gas in the atmosphere of Venus Monday unleashed global excitement about the possibility of the presence of life forms on the neighboring planet. In addition to being produced in industrial processes, phosphine, a colorless but malodorous gas, is known to be produced only by some species of bacteria that survive in the absence of oxygen.

In a paper published in Nature Astronomy, a team of scientists reported trace amounts of phosphine at a concentration of about 20 parts per billion, thousands to millions of times more than might be expected otherwise.

So is there life on Venus?

Nobody says that as of now. What scientists have discovered is the presence of a chemical that is known to be produced only through a biological process and not through any natural chemical process. There are other ways this chemical could be produced, for example in the underbelly of volcanoes or meteorite activity, but that would have been demonstrated at much lower concentrations. In any case, scientists have ruled out all of those known possibilities that could be attributed to the presence of that gas.

In fact, this discovery was made in 2017 and scientists checked and double-checked their data for the past three years before deciding to make it public.

The abstract of their paper in Nature Astronomy says that this phosphine presence is “inexplicable” after a comprehensive study of all other possible sources and “production routes in the atmosphere, clouds, surface and subsurface of Venus, or by the discharge of lightning, volcanic or meteorites “.

So the only possible explanation for the origin of this phosphine, based on our current knowledge, could be in biological processes, the way it is produced on Earth, by some microbes.

During an announcement Monday, scientists were very careful to emphasize, repeatedly, that this was not a confirmation of the presence of life on Venus.

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This artist’s rendering shows an actual image of Venus, taken with ALMA, in which ESO is a partner, with two overlapping spectra taken with ALMA (in white) and the James Clerk Maxwell Telescope (JCMT; in gray). The drop in the JCMT spectrum of Venus provided the first indication of the presence of phosphine on the planet, while the more detailed spectrum of ALMA confirmed that this possible marker of life is actually present in the atmosphere of Venus. As the phosphine molecules float in high clouds on Venus, they absorb some of the millimeter waves that occur at lower altitudes. By observing the planet in the millimeter wavelength range, astronomers can pick up this phosphine absorption signature in their data, as a drop in light from the planet.

So why is it important?

This is the most credible evidence yet for the possibility of life outside of Earth. Scientists say it is more significant, for example, than the discovery of water on the Moon or Mars.

“In the search for extraterrestrial life, this is the biggest find, hands down. Of course this cannot mean that there is indeed life on Venus, or anywhere else, but if you are a scientist looking for life forms on other planets, I think this is your first real breakthrough, ”said IISER’s Dibyendu Nandi. , Calcutta.

This is how Professor Sara Seager from the Department of Physics at the Massachusetts Institute of Technology, who is one of the authors of the study, also described the finding. She said the phosphine detection had lifted Venus “higher on the scale of interesting targets” where the possible presence of life forms can be explored.

But Venus can’t stand life, right?

There are several things we know about Venus that make life as we know it unsustainable on that planet. The temperature of Venus is too high and its atmosphere is very acidic, just two of the things that would make life impossible.

But Somak Raychaudhuri, director of the Pune-based Interuniversity Center for Astronomy and Astrophysics, suggested this phosphine could be a holdover from a time when Venus was a much more hospitable place.

Look, this find opens up a lot of interesting possibilities. We don’t know how long the phosphine molecules survive. Also, we know that Venus has not always been as inhospitable as it seems now. So one of the possibilities, if we wanted to explore the question of the presence of life on Venus, it could be if this phosphine is actually something left over from a time when the planet did harbor life forms. These are open questions at this time. All of these will be explored. What we have now is just a foothold at the door. Now we can probe with greater enthusiasm, ”he said.

“Personally, I would not class this discovery in the same league as the discovery of the first planet, or the recent confirmation of gravitational waves, for example, but it is certainly not as tasteless as some water molecule sign found on some planet. In fact, in that way it is greater than the evidence of water. Water is only circumstantially related to life. It is not produced by life. Phosphine is produced through biological processes. So this is significant, certainly, and nothing like this has been discovered so far, “he said.

Varun Bhalerao of IIT Bombay said it was too early to consider this as evidence of extraterrestrial life. “If you look at the article they have published, the scientists themselves say something like, look, we found phosphine, but we don’t know if it means life. It’s very interesting, and extraterrestrial life is certainly plausible, but based on this finding, I don’t think I’m holding my breath from microbes on Venus, just yet. Many strange molecules have previously been found in strange places in space, where they were not expected, “he said.

What could this mean for the Venus missions?

The find may further spark interest in space missions to Venus. Missions to Venus are not new. Spaceships have been approaching the planet since the 1960s and some of them have even landed. In fact, the Indian Space Research Organization (ISRO) is also planning a mission to Venus, tentatively named Shukrayaan, in the near future. As of now, the plan is still on the drawing board.

All future missions to Venus would now be in tune with the investigation of further evidence for the presence of life.

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